This allows using icu data, bundled in the icudtl.dat file,
to be loaded automatically from a default location
side-by-side with the executable.

The v8 stand-alone default is still to use statically
linked ICU data, but this will be switched in a separate
follow-up CL.

BUG=chromium:616033
LOG=y

Review-Url: https://codereview.chromium.org/2042253002
Cr-Commit-Position: refs/heads/master@{#36823}